ITTO20000494A1 - METHOD FOR THE MANUFACTURE OF AN EJECTION HEAD OF LIQUID DROPS, PARTICULARLY SUITABLE FOR OPERATING WITH CHEMICALLY AGGLE LIQUIDS - Google Patents

Abstract

A method for manufacturing an ejection head ( 10 ) or ejector suitable for ejecting in the form of droplets ( 16 ) a liquid ( 14 ) conveyed inside the ejection head ( 10 ), comprising a step of producing, from a silicon wafer, a nozzle plate ( 12 ) having at least one ejection nozzle ( 13 ); a step of producing, from another silicon wafer, a substrate ( 11 ) having at least one actuator ( 15 ) for activating the ejection of the droplets of liquid through the nozzle ( 13 ); and a step of joining the nozzle plate ( 12 ) and the substrate ( 11 ) together to form the ejection head, wherein this joining step comprises the production of a junction ( 25 ), made by means of the anodic bonding technology, between the substrate ( 11 ) and the nozzle plate ( 12 ), in such a way that, in the area of this junction ( 25 ), the ejection head ( 10 ) does not present structural discontinuities, and also possesses a resistance to chemical corrosion by the liquid ( 14 ) contained in the ejection head ( 10 ) at least equal to that of the silicon constituting both the substrate ( 11 ) and the nozzle plate ( 12 ). The method of the invention may be applied for manufacturing an ink jet printhead ( 110 ), having one or more nozzles ( 113 a , 113 b, etc.), which has the advantage, with respect to the known printheads, of also being suitable for working with special inks characterized by high level chemical aggressiveness. In general, the ejection head of the invention, thanks to its structure which is globally highly robust and also chemically inert in the area of the junction ( 25 ), can be used advantageously with various types of liquids, even with marked chemical aggressiveness, in different sectors of the art, for example for ejecting paints on various types of media, generally not paper, in the industrial marking sector; or for ejecting in a controlled way droplets of fuel, such as petrol, in an internal combustion engine.

Description

Description of the industrial invention entitled:

"METHOD FOR MANUFACTURING A LIQUID DROPS EJECTION HEAD PARTICULARLY SUITABLE FOR WORKING WITH CHEMICALLY AGGRESSIVE LIQUIDS, AND RELATED EJECTION HEAD"

TEXT OF THE DESCRIPTION

Area of the invention

The present invention relates in general to the sector of ejection heads for ejecting liquids in the form of drops, and in particular to an ejection head provided with a structure such as to make this ejection head very suitable for operating with liquids having a high degree of aggressiveness. from the chemical point of view.

The present invention also refers to a method for manufacturing an ejection head having a special resistance to chemically very aggressive liquids, so as to be advantageously used in combination with this category of liquids.

Technical background of the invention

The ejection head, hereinafter also referred to simply as an ejector or injector, according to the invention has such characteristics that make it advantageous to use it in many industrial sectors, even with completely different specificities, characteristics and problems from one sector to another.

In particular, among these possible fields of application, we cite, purely by way of example, that of ink jet printing, or that of fuel injection in an internal combustion engine.

As will become clear in the following description, the ejection head of the invention has remarkable similarities, both structural and functional, with a thermal ink-jet printing head, of the type operating on the basis of the so-called jet printing technology. bubble ink. This type of print heads are widely known in the field of inkjet printing technologies, where they have been applied in multiple solutions, and continue to be the subject of significant developments.

Therefore, for completeness and in order to facilitate the understanding of the present description, and also in consideration of the fact that the ink jet printing sector constitutes, as already mentioned, one of the possible and main fields of application of the present invention, general characteristics of these bubble-type thermal inkjet printing heads and some of their most recent developments will be briefly described below. As is known, in the print heads operating with bubble-type ink jet technology, the ink contained in the print head is brought to the boil by thermal actuators consisting of electrical resistances which are fed with suitable current pulses to activating, within the ink itself, the rise of a vapor bubble, which, expanding, causes the ejection of the drops through a plurality of nozzles of the print head.

The print heads operating with bubble technology can be divided into two broad categories, according to their structure, which are indicated respectively with the English expressions "top shooter" and "edge shooter". In the first type, the nozzle consists of an opening placed immediately above the thermal actuator and separated from the latter by a chamber filled with ink, so that the expansion of the vapor bubble is used perpendicular to the thermal actuator. to emit the drop through that opening. In the second type, the thermal actuator is arranged along the wall of a duct a short distance from the outlet section towards the outside of the duct itself, so that the expansion of the vapor bubble is used transversely with respect to the actuator to emit the drop laterally through the outlet section of the duct.

This bubble technology has been established in the printing industry for many years now, and is successfully applied to multiple models of inkjet printheads for both black and white and color printing. In particular, inkjet print heads that operate according to this technology are evolving towards ever greater integration and complexity, with the aim of including an increasing number of circuits, nozzles and functions, so as to achieve speed and definitions. increasingly high printing. One of the most recent examples of this technical development is constituted by the so-called monolithic print heads, i.e. thermal inkjet heads in which the nozzle plate is made, not as a separate part, but jointly with the other parts of the print head, in particular with those parts which constitute the driving circuits of the actuators and the hydraulic network for conveying the ink inside the print head.

Therefore, in these monolithic heads, the nozzle plate is not a piece that is made separately and assembled at the end of the print head manufacturing process, but rather a part that is progressively formed as part of this manufacturing process, whereby each head of printing acquires a typically monolithic structure integrating the various parts.

Parallel to the continuous evolution of bubble inkjet thermal print heads, the inks that can be used on these heads have also undergone a significant evolution, which has led them to constantly improve their quality and reliability.

In general, the evolution of the print heads has been accompanied by a corresponding evolution of the inks in order to seek ever better combinations between the print media intended to receive the ink drops, the structural characteristics of the head, and the chemical characteristics. of the inks.

Typically this ink research has evolved with the aim of formulating inks that are capable of both improving print quality on an ever-growing range of substrates, and optimally coupling with new print head structures. press that were introduced over time.

In this way, both black and colored inks were formulated, capable of minimizing the problem of nozzle clogging, due to the sedimentation of the pigments contained in the inks, despite the ever-increasing miniaturization of the print heads and the reduction in diameter. nozzles to get smaller and smaller drops.

Furthermore, the research has made it possible to define optimal combinations between inks and materials used in the manufacture of the heads, with inks and materials compatible with each other, i.e. capable of not activating unwanted reactions, and of maintaining their nominal characteristics over time, so as not to have any effects. negative effects on the operation and reliability of the print heads. In particular, this research directed, as mentioned, to constantly improve the combination between inks, print media, and print heads, has obviously been directed towards the formulation of inks having a low or almost zero degree of chemical aggressiveness, or towards inks without of substances capable of attacking, corroding and reacting, even minimally, with the various materials used in the manufacture of the heads and lapped by the same inks.

For example, we tried to avoid those inks containing substances that could interact with the organic compounds usually used to make the junctions between the parts of the head. However, in this way, recent research on inks has actually resulted in a certain consolidation, for the use on print heads, of inks characterized by a zero or almost zero level of chemical aggressiveness.

At the same time, the possibility of using these print heads in combination with particular types of ink and / or liquids in general has been neglected which, despite being widely applied and able to give excellent results in certain fields, even different from actual printing. , however, they had characteristics of chemical aggressiveness incompatible with the structure of the print heads that were developed, and in particular they contained aggressive substances certainly able to corrode them and compromise their functioning over time.

On the other hand, as you can easily imagine, it could be very useful and advantageous to have a new inkjet print head, both of the type based on bubble technology and also on other technologies, having the ability to operate with inks, perhaps already successfully used in various applications, even dissimilar to printing on paper, but unfortunately containing corrosive and / or aggressive substances such as to damage the structure and materials of the bubble-type thermal inkjet heads over time, currently known. In fact, in this way the application possibilities for these print heads could be considerably expanded, considering the new properties, the salient characteristics and the performance advantages that these corrosive substances could confer on the inks used with them. Unfortunately, as mentioned, in reality the known inkjet print heads do not have a structure capable of resisting corrosive agents that may be present in the inks used with the same print heads, so in this hypothetical case they should be encountering rapid decay.

For example, as is known, inks known to be typically aggressive, for example containing urea, and / or having certain acid PHs, certainly cannot be used on current thermal heads, because they would certainly damage the junctions and the bonding areas between the various states. that make up the head structure.

Still in the art there are sectors, even completely different from that of inkjet printing and the related print heads, in which it is necessary to eject liquids in the form of drops, preferably even very small ones, and in which these liquids to be ejected are particularly aggressive from the chemical point of view, and in any case have a composition incompatible with the structure of the currently known print heads.

One important of these sectors, which has already been mentioned above, is that of the injection of a fuel, such as diesel or petrol, into the combustion chamber of an internal combustion engine. In this sector, the solutions normally adopted for fuel injection include mechanical injectors, which however have the drawback of not reaching a sufficient degree of miniaturization of the drops, or rather that degree of miniaturization that would allow a better and more precise dosage. fuel, and therefore to obtain better engine performance, such as a higher thermal efficiency.

Therefore, at least potentially, this sector could benefit from inkjet technology which, compared to traditional fuel ejectors, is capable of obtaining much smaller liquid droplets in volume, as well as obtaining a better and more efficient control of the volume quantity of liquid ejected in the form of drops.

Still another sector, in which the need to dose in a precise and controlled way of particularly aggressive liquids from the chemical point of view may arise, is the biomedical one.

Summary of the invention

Therefore, the general purpose of the present invention is that of realizing a new ejection head which, while presenting some similarities with the known inkjet print heads, substantially innovates with respect to them, and in particular possesses characteristics such as to make it possible and It is advantageous to use it in combination with particularly aggressive liquids from the chemical point of view, even in industrial sectors very different from ink jet printing, and for example in the sector of injection of a fuel in an internal combustion engine.

This object is achieved by the ejection head and by the corresponding manufacturing method having the characteristics defined in the main independent claims.

A more specific object of the present invention is to provide an ink jet print head, of the type operating both with bubble technology and with other technologies, which can be used without drawbacks with aggressive inks known to be capable of reacting chemically with and / or to corrode the materials, typically organic-based ones, currently used in the manufacture of print heads, so as to allow, at least potentially, an expansion of the possibilities of industrial application of the technologies and concepts developed in connection with these print heads known to sectors hitherto excluded from such technologies and concepts.

These and other objects, characteristics and advantages of the invention will become evident on the basis of the following description of a preferred embodiment thereof, given by way of non-limiting example, with reference to the attached drawings, of which:

Fig. 1 is a schematic sectional view of a head for ejection of drops of liquid according to the present invention;

Fig. 2 is a synthetic flow chart of a method according to the present invention for manufacturing the ejection head of Fig. 1;

Fig. 3 (section a-g), composed of Fig. 3a and Fig. 3b, is a sectional view showing in sequence the various steps for manufacturing a plate with nozzle of the ejection head of Fig. 1;

Fig. 4 (section a-c) is a sectional view showing the final steps for making the structure of a substrate carrying an actuator of the ejection head of Fig. 1;

Fig. 5 is an operating diagram that refers to a fixing operation, carried out using the "anodic bonding" type technology, to weld the nozzle plate of Fig. 3 with the substrate of Fig. 4;

Fig. 6 shows a first example of application of the invention concerning a print head provided with a plurality of nozzles and suitable for ejecting ink drops;

Fig. 7 shows a silicon wafer used to manufacture a plurality of nozzle plates of the print head of Fig. 6;

Fig. 8 shows another silicon wafer used to fabricate a plurality of substrates of the print head of Fig. 6; And

Fig. 9 shows a second example of application of the ejection head manufactured with the method of the invention, in which the ejection head is provided for ejecting fuel drops in an internal combustion engine.

Description of a preferred embodiment of the invention

With reference to Figs. 1 and 2, a head for ejection of drops of liquid, also hereinafter referred to as an ejection head, or ejection device, or more simply an ejector, manufactured according to the method of the present invention, is generically indicated with 10, and comprises a substrate 11, also called actuation support, which carries at least one actuator 15, also called ejection actuator hereinafter; a nozzle plate 12, also called with English terminology "orifice piate", which is provided with at least one nozzle 13 and is rigidly connected with the substrate 11 along a junction area 25; and a hydraulic circuit 21, arranged inside the head 10, which has the function of containing and conveying a liquid 14 in the area 10 between the actuator 15 and the nozzle 13, so that they are both lapped by the liquid 14.

The ejection head 10 is rigidly fixed along the substrate 11 on a support 30. The actuator 15 is positioned, along the substrate 11, in an area adjacent to the nozzle 13, and is adapted to periodically activate, in the volume of liquid 14 which separates it from the nozzle 13, a pressure wave, or in general a pumping effect, such as to cause the emission of a plurality of drops 16 formed by the liquid 14, through the nozzle 13.

For this purpose, the actuator 15 is designed to be piloted directly by means of suitable electrical impulses or signals, each corresponding to an ejected droplet, which are governed by an electronic control unit 19 of the ejection head 10.

The actuator 15 can also be associated with actuation circuits, arranged between the actuator and the control unit 19, which, under the control of the control unit 19, have the specific function of generating the pulses which they directly control the actuator 15 to generate the drops 16.

In Fig. 1, the line 18 schematically represents the electrical connection, between the control unit 19 and the actuator 15, which has the function of transmitting the direct signals to control the actuator 15 to cause the ejection of the drops 16 .

In particular, the hydraulic circuit 21 comprises a first supply duct 24, for conveying the liquid 14, which develops through the substrate 11; a second supply conduit 22 which is formed along the nozzle plate 12 and which is in communication with one end of the first conduit 22; and at least one chamber 20, also formed on the nozzle plate 12, which is adjacent to both the actuator 15 and the nozzle 13.

The chamber 20 is adapted to be fed with the liquid 14 through the adduction duct 22, and defines an internal space in which the liquid 14 is subjected to the pressure wave generated by the actuator 15 to be ejected through the nozzle 13.

Furthermore, the ejection head 10 is associated with a tank 17, containing a certain quantity of the liquid 14, which constitutes a reserve for the liquid 14 to be fed to the chamber 20 of the ejection head 10, and which for this purpose is in communication with the hydraulic circuit 21, through a supply duct 23.

In this way the ejection head 10 can continuously receive the liquid 14 from the tank 17, so that it is ejected in the form of drops 16 towards the outside of the ejection head 10 through the nozzle 13.

The technologies used to generate, in the liquid 14, the aforementioned pumping effect which determines the ejection of the drops 16 of liquid can be of various types and are based on different principles. For the sake of simplicity, in the present description, reference will preferably be made to the bubble type ejection technology, widely known and used in the printer sector, which is based on the generation by the actuator 15, in the area of the nozzle 13. of a microbubble of liquid vapor, which expanding causes the ejection of a drop of liquid through the nozzle 13. It is however clear that the description to be made should not be understood as tending to limit the scope of the present invention to this particular liquid drop ejection technology.

For example, as an alternative to bubble technology, the pumping effect for ejection of the drops could be obtained through the deformation of a piezoelectric type actuator.

Now, in the context of the aforementioned bubble technology, the actuator 15 is constituted by a resistor which, in use, is driven by the control unit 19 with a short current pulse such as to determine, due to the joule effect, a rapid heating of the same resist 15.

In this way the liquid 14 disposed in the immediate vicinity of the resistor 15 is brought to evaporation, and therefore causes the rise of a vapor bubble, derived from the same liquid 14, which expanding exerts a pumping effect in the direction of the nozzle 13 to determine through the latter, the ejection of a drop 16.

Then, at the end of the impulse, due to the concomitant cooling of the resistor 15, the vapor bubble collapses, so that the liquid 14 adjacent to the resistor 15 returns to its initial conditions, and the resistor 15 can be activated again with a new impulse. to cause the ejection of a new drop 16. In summary, this cycle is repeated periodically, driving the resist 15 with a predetermined succession of pulses which determine the generation of as many bubbles of vapor adjacent to the resist 15, and the ejection of corresponding drops 16 through the nozzle 13.

As shown in Fig. 1, the nozzle 13 is arranged in front of the resistor 15, so that the expansion of the vapor bubble is used in the normal sense of the resistor 15 to eject the drop 16. This arrangement, as already mentioned, it is often called "top shooter" in English terminology, and is typical of an important category of ejection heads which are based on bubble technology. However, the relative arrangement between the ejection actuator and the nozzle may also be different from that shown in Fig. 1, without thereby departing from the present invention.

As described in detail below, also the liquid 14 used on the ejection head 10 to be ejected in the form of drops can be of different types, and have completely different compositions from one type of liquid to another, depending on the specific sector in which the ejection head 10 is applied, and therefore specific characteristics that the liquid must possess in relation to that particular sector. The nozzle plate 12 and the substrate 11 constitute the fundamental parts of the present ejection head 11, and are made through two distinct procedures, indicated in Fig. 2 respectively with 31 and 32, to be subsequently assembled and rigidly connected to each other, during a step 33, so as to form the ejection head 10.

For clarity, the two manufacturing processes 31 and 32, respectively of the nozzle plate 12 and of the substrate 11, will be described separately, starting with that relating to the nozzle plate 12.

With reference to Fig. 3, this process comprises an initial step, shown in section (a) of Fig. 3a, in which a silicon plate 51, also called in English "wafer 'and having two opposite faces indicated respectively with 51 a and 51, is glued by means of an adhesive substance on a support 52, for example along the side 51 b.

The wafer 51 is readily available on the market and has a normalized shape, for example round disk with a diameter of 3 "and an indicative thickness of 75 µm.

The support 52 can also consist of a known type of wafer, although significantly thicker than the wafer 51 used to manufacture the nozzle plate 12.

For example, the support 52 can be made with a 4 "diameter round wafer, with a thickness of 0.5 mm, either of the standard type of silicon, or of glass or ceramic.

The wafer 51 is externally oxidized, so as to present along its two opposite faces, 51a and 51b, a thin layer 55 of silicon oxide SiO2. for example

often 0.3 0.4 pm.

After fixing on the support 52, the wafer 51 is covered in a known way, along the free face 51 a opposite to that 51 b glued on the support 52, with a thin layer 53 of a light-sensitive substance, also called in English "photoresist ”, Often 1-3 pm.

In particular, the photoresist that constitutes the layer 53 is of the positive type, that is, it is such as to be resistant to and not attackable by certain substances under normal conditions, and on the other hand to become easily dissolvable and removable by these substances, if exposed to light radiation. .

According to known techniques and as shown in Fig. 3a - sect. (b), after spreading on the wafer 51 this positive photoresist layer 53 is subsequently illuminated with a light 49 through a special mask 50 having a specific configuration which corresponds to the positive image of those parts of the hydraulic circuit 21, i.e. the supply 22 and chamber 20, which will be formed on the nozzle plate 12.

In this way the layer 53 is impressed so as to become removable during the subsequent operation only in the areas illuminated by the light 49.

Conveniently, in order to achieve economies of scale and improve the efficiency of the production process, the wafer 51 can be used for the manufacture of a plurality of nozzle plates 12, each corresponding to an elementary area of the wafer 51.

For this purpose, the mask 50 is arranged with a configuration which is constituted by a plurality of identical profiles, each reproducing a hydraulic circuit 21 to be created on a corresponding elementary area of the wafer 51. Therefore the positive photoresist 53 is illuminated through the mask 50 , and therefore it becomes removable, along a plurality of identical areas, one for each elementary area of the wafer 51, which correspond to the profiles of the mask 50.

For simplicity, Fig. 3a - sect. (b), as well as the following ones, refer to and represent the structural changes that occur only in an elementary area of the wafer 51, it being however clear that what is shown in each of these figures is to be considered repeated exactly in each of the other areas wafer elements 51.

Then, using known techniques, the photoresist layer 53 is developed, removing from it the areas exposed to the light and therefore not resistant, so as to discover, in correspondence with these areas, the underlying layer 55 of SiO2, as shown in Fig. 3a - section (c).

Subsequently, the wafer 51 is subjected to an etching operation, which has the purpose of removing, in correspondence with the areas not protected by the upper photoresist layer 53, the surface thickness 55 of SiO2, so as to uncover the underlying silicon part. .

Typically this etching operation to remove SiO2 is carried out in a liquid bath, or in any case in a humid environment, and for this reason it is often also identified with the English expression "wet etching" or simply "wet". Then the outer photoresist layer 53 is removed. In this way the SiO2 layer 55 forms the protective mask for the subsequent etching operation of the silicon constituting the wafer 51.

According to a variant of the process described up to now, the initial wafer can be devoid, along its faces, of the surface layer of SiO2, and therefore consist only of pure silicon. In the latter case, the photoresist layer is deposited directly on the silicon of the wafer and subjected to the same operations of illumination, development, and removal already described in relation to the previous case of the oxidized wafer on the surface, so as to form a protective mask , for the subsequent step of etching the silicon of the wafer, which is exactly equivalent to that, carried out by means of the S1O2 layer, relating to the previous case. For simplicity, only the case of the wafer 51 provided with the two SiO2 surface layers is shown in Fig. 3.

In both cases described above, after the formation of the protective mask for the silicon of the wafer 51, as mentioned, either by means of the S1O2 layer, or by means of a photoresist layer, the wafer 51 is subjected to one or more further operations of incision, which have the purpose of selectively removing the silicon of the wafer 51 up to a certain depth, so as to form the chamber 20 and the supply duct 22, of the hydraulic circuit 21, which are present on the nozzle plate 12.

This incision phase, shown in Fig. 3a - sect. (d), is made by means of special equipment in a vacuum environment, where the wafer 51 is subject to the action of agents in the gaseous state or plasma which combine with the unprotected silicon of the wafer 51 to corrode it and remove it to the depth desired.

Therefore, in contrast to the etching phase mentioned above and carried out in a wet environment, or "wet etching", this etching phase is often identified with the English word "dry etching".

For example, in this phase the wafer 51 is hollowed to a depth of about 10 ÷ 25 μm, so as to form a recess 54 consisting of two portions 54a and 54b, corresponding respectively to the chamber 20 and to the supply duct 22, in which the portion 54a has an approximately square shape in plan.

Subsequently, a thick layer 56 of negative photoresist, consisting for example of negative photoresist type SU8, named after the manufacturer, is deposited, with a known method, along the entire extension of the non-glued side 51 a of the wafer 51, in so as to completely cover the recess 54 as well. This layer 56 has a thickness of approximately 15 ÷ 30 μm, to allow covering the step defined by the recess 54.

It should be noted that this negative photoresist constituting the layer 56 has an opposite behavior to that of the positive photoresist constituting the previous layer 53, and therefore in normal conditions it can be dissolved in contact with certain substances, while, if illuminated, it acquires a certain resistance to these substances. .

Then, as shown in Fig. 3b - sect. (e), this thick layer 56 is illuminated, through a determined mask 59, so as not to receive the light 49 in correspondence with that portion, of the same layer 56, indicated with 58 and having a square shape in plan, which fills the portion 54a, of the recess 54, corresponding approximately to the chamber 20.

Subsequently, according to what is illustrated in Fig. 3b - sect. (f), the negative photoresist layer 56 is developed and excavated, with known techniques, so as to remove the unlit portion 58 and thus delimit, along the bottom of the recess 54, adjacent to the chamber 20, a narrow area 61, to square shape and not protected by the layer 56, corresponding to the area of the nozzle 13 that will be formed.

At this point, as shown in Fig. 3b - sect. (g), the wafer 51 is subjected to a further etching process, which has the purpose of hollowing out the silicon of the wafer 51 only in correspondence with the restricted area 61, square, defined along the bottom of the recess 54.

This etching is of the wet type, being performed in a humid environment, for example using a compound such as KOH, and is also called anisotropic, since it develops along the crystallographic axes of the silicon that constitutes the wafer 51.

In particular, this incision causes the formation of a blind hole 62, having a pyramidal shape, as shown in the plan view of the same Fig. 3b - sect. (g).

More in detail, taking into account the side of the uncovered square area 61, the thickness, equal to 50 μm, of the silicon wall to be engraved, and the inclination, equal to about 54 °, of the crystallographic axes of the silicon, the The incision develops in such a way as to form a pyramidal blind hole 62 on this wall, leaving a thin residual layer of silicon, indicated with 60, at the bottom of the blind hole 62.

At this point, after removing the thick layer 56 of photoresist, the wafer 51 is unglued, along the side 51 b, from the support 52, and then cleaned and subsequently glued along the opposite side 51 a on the same support 51 or on another support similar.

Subsequently, as shown in Fig. 3b - sect. (h), the wafer 51 is covered along the side 51 b, now free, with a layer 57 of positive photoresist, represented by a dotted line, which is subsequently illuminated with a special mask, impressed and developed, with the same techniques already seen above, so as to protect the entire extension of the layer 55 of silicon oxide SiO2 arranged along the side 51b, with the exception of a narrow circular area adjacent to the wall 60 and corresponding to the nozzle 13.

Then the wafer 51 is subjected to a further "wet" type etching process, ie through a chemical bath, to remove the circular, unprotected area of the SiO2 silicon oxide layer 55, and uncover an underlying and corresponding circular area wafer silicon 51.

In this way the layer 55 forms a protective mask for the silicon of the wafer 51 during the subsequent dry etching operation.

Naturally, if the wafer 51 was not originally provided with the SiO2 layer, this protection mask is made with a photoresist layer, in a similar way to what has already been seen previously.

In particular, in this case, the photoresist thickness is chosen with an adequate thickness, in relation to the thickness of silicon to be engraved in the subsequent phase, to allow a correct realization of this etching phase.

Then, during a "dry" etching process, the uncovered circular area of the silicon of the wafer 51, that is, not protected by the layer 55, is engraved, so as to hollow out the wall 60 and form through it a through hole 63 corresponding to the 'nozzle 13.

Finally, the wafer 51, which, it should be remembered, has undergone the operations described above for each of its elementary areas, is cut into individual units corresponding to these areas, and each constituting a nozzle plate 12.

Subsequently, the individual nozzle plates 12 are washed and checked to verify that they do not contain defects, and that they have been formed correctly. In this way, starting from the wafer 51, the structure constituting the nozzle plate 12, which is shown in Fig. 3b - sect. (i), both laterally in section and in plan.

The process 32 for manufacturing the substrate 11 largely follows a known sequence and adopts technologies which are also known, and therefore will not be described in detail.

It is only recalled that this process 32 starts from the availability of a silicon support or wafer 70, similar to that used to manufacture the nozzle plate 12, but with a considerably greater thickness, for example 0.5 mm, and has the purpose of making a this support 70, in addition to the actuator 15, certain protective layers having the function of protecting the actuator 15 itself so as to prolong its operating life.

During the process 32 the appropriate track, or tracks, are also made for the electrical connection of the actuator 15 with the circuits used to drive it.

In particular, as already mentioned, the process 32 can also comprise the realization, on the silicon wafer 70, of specific auxiliary circuits, often called with the English term "driver", adapted to be conditioned by the control unit 19 to generate the pulses to be sent directly to the actuator 15 to activate the ejection of the drops 16.

Similarly to the nozzle plate 12, and in order to achieve economies of scale and improve the efficiency of the production cycle of the substrate 11, a single silicon wafer 70 can be used to simultaneously produce a plurality of substrates 11, identical to each other, and each corresponding to an elemental area or portion of the original silicon wafer 70.

For clarity, the structure of the substrate 11 which is made by means of the known operations mentioned above and which corresponds to an elementary portion of the wafer 70 is shown in Fig. 4 - section. (to).

In particular, this structure comprises a base layer 71 of silicon substantially corresponding to the thickness of the initial starting wafer 70; a zone 72, made with MOS technology, which comprises a series of circuits or drivers for controlling the operation of the ejection head 10; a thin layer 73 of silicon oxide S1O2 selectively grown over the silicon layer 71, and in particular missing along the zone 72 with the MOS circuits; a thin resistive film of limited extension or resistor 74, constituting the actuator 15; one or more tracks, not shown in the drawings and extending in the direction normal to the plane of Fig. 4, to electrically connect the resistor 74 with the arcades of the zone 72; a protection layer 76 composed of silicon nitride and silicon carbide and deposited over the resistor 74; and a layer 77, consisting of tantalum Ta, arranged over the nitride / carbide layer 76 in the area of the resistor 15.

The Ta layer 77 essentially has the function of protecting the resistor 74 against wear caused by the mechanical stresses to which the resistor 74 is subjected during the operation of the ejection head 10.

Typically these stresses are caused by the cavitation phenomenon which occurs due to the pumping of the liquid 14, determined by the resistor 74, to eject the drops 16,

As will be seen better below, this tantalum layer 77 is intended to be advantageously used also during the subsequent joining operation of the substrate 11 with the nozzle plate 12, to form the ejection head 10, and this purpose is the layer 77 of tantalum is deposited over the silicon wafer 70 so as not only to cover the area of the resistor 74, but to extend laterally along the area where the junction will be made.

Furthermore, again for this purpose, the layer 77 is formed in such a way as to have, along its edge, a portion 77a, which is arranged externally with respect to this junction area.

Differently from the known art and in order to prepare the substrate 11 for the subsequent operation, described below, of joining with the nozzle plate 12, the structure of the substrate 11 also comprises, along certain junction areas, an external surface layer 78 of glass borosilicate, deposited on top of the tantalum layer 77.

As shown in Fig. 4 - sect. (b), this layer 78 of borosilicate glass is initially deposited in a continuous manner over all the areas of the original wafer 70, so as to completely cover the tantalum layer 77 made on these areas.

In particular, layer 78 has a thickness of 1 ÷ 5 μm, and is made of borisilicate glass of the Pyrex 7740 type, or of the Schott 8329 type, containing sodium and lithium ions, with a thermal expansion coefficient equal to and therefore very close to that of silicon which is of

In this way, the layer 78 of borosilicate glass and the silicon of the wafer 70 are coupled in an optimal way without causing mechanical stresses to arise in the junction area.

The deposition of the outer layer 78 of borosilicate glass on the substrate 11 is carried out in a known way, for example by means of the process known by the English term of "sputtering RF", in which the borosilicate glass is atomized and sprayed on the substrate 11.

The deposition of layer 78 can also be carried out by means of the procedure known by the English term of "electron-beam evaporation", in which an electronic ray is irradiated on an electrode made of borosilicate glass, so that the borosilicate glass evaporates and deposits on the substrate 11.

Compared to sputtering, the electron-beam evaporation process has the advantage of being faster, that is, of being able to deposit a greater quantity of material in the unit of time, and also of ensuring a better stoichiometric control of the deposited layer 78. of borosilicate glass.

Then this continuous layer 78 of borosilicate glass is etched with known techniques in order to uncover the resist area 74, and to restrict the layer 78 to the area of the substrate 11 intended to be coupled with the nozzle plate 12.

In this way, the borosilicate glass layer 78 forms a kind of frame around the resist 74. For this purpose, the continuous layer 78 is first covered with a layer of positive photoresist, which is then selectively illuminated, and finally removed in a correspondence of the illuminated areas, so as to define a protection mask for the underlying layer 78.

Subsequently, still with known techniques and for example by means of a dry etching step, the layer 78 of borosilicate glass is removed along the areas not protected above by the photoresist.

In this way the structure is obtained, represented in Fig. 4 - sect. (c), which constitutes the substrate 11.

Naturally, if a single original wafer 70 is used to make several substrates 11, this structure is duplicated in the various elementary areas of the silicon wafer 70.

In summary, this structure comprises by way of example a residual layer 78a of borosilicate glass, which is obtained by selective etching of the original continuous layer 78 and is arranged laterally with respect to the resist 74, so as to reveal the portion of the layer 77 of tantalum which protects the resist. 74, and a joint or welding surface 79 for coupling the substrate 11 with the nozzle plate 12 is also to be defined.

In order to ensure the best results during the subsequent step of joining the substrate 11 with the nozzle plate 12, a step which is carried out by means of the so-called anodic welding technology as described in detail below, preferably the layer 78 of borosilicate glass is subjected to a planarization operation along the free surface intended to couple with the nozzle plate 12.

This operation has the purpose of reducing to a minimum the roughness of the surface of the layer 78 and is carried out for example by using a planarization process called CMP, from the English expression "Chemical-Mechanical Polishing".

In fact, as is known, the anodic welding process requires an exceptional degree of planarity of the surfaces which must be coupled with this process.

Unfortunately the wafer 70, during the operations, for the formation of the substrate 11, which precede the deposition of the borosilicate glass layer 78, inevitably acquires a certain degree of roughness, which the same layer 78 of borosilicate glass necessarily reproduces and amplifies.

Therefore, the CMP planarization process has the purpose of remedying this progressive increase in roughness on the wafer 70, ensuring a very high degree of planarity of the surface of the layer 78 of borosilicate glass intended to couple in contact with the nozzle plate 12.

In particular, this CMP-type planarization process can be carried out after the spreading of the continuous layer 78 of borosilicate glass, and before its etching to define the residual layer 78a and the corresponding junction surface 79.

As already anticipated, and according to a characteristic of the present invention, the plate 12 with the nozzle 13 and the substrate 11, after having been manufactured separately from each other as described above, are rigidly joined by means of a joining process based on the so-called anodic bonding technology, frequently also called with the corresponding English term "anodic bonding".

For information, it should be noted that anodic welding is a joining technology that has been developed and perfected in recent years, and which is currently being applied to an ever-increasing extent in many fields of technology, in particular in the field of microstructures, also indicated with the acronym MEMS from the English expression "Micro ElectroMechanical System", in order to create a stable and effective junction between two parts that make up a microstructure.

For example, this anodic welding joining technology is advantageously used to structurally join two silicon wafers together, in which case it is also indicated with the English expression "silicon-to-silicon anodic bonding".

As is known, the anodic welding technology is used to join two surfaces having a high degree of flatness, and is essentially based on the principle of placing the two surfaces to be joined in mutual contact at a suitable pressure and temperature, and therefore applying a certain potential they.

In this way, in fact, the junction area becomes the seat of suitable electrostatic charges which tend to mutually attract and penetrate the molecules of the two surfaces, so as to achieve structural cohesion between them.

Often this technology requires that the surfaces intended to be coupled in contact are adequately prepared, for example by depositing on at least one of them a suitable layer of material.

Furthermore, as already mentioned, this technology also requires that the two surfaces to be coupled are extremely flat and free of roughness, i.e. perfectly matching along the contact area, so that the phenomenon of interpenetration and structural cohesion between the respective molecules can take place.

Further details and information on anodic bonding technology can be found in the following publications cited below for reference purposes:

“Field Assisted Glass-Metal Sealing”, published on p. 3946, of volume 40, No. 10, September 1969, of the journal “Journal of applied phisics”;

"Fabrication of a silicon-Pyrex-silicon stack by a.c. anodic bonding published on p.

219 and following, of No. A 55, 1996, of the magazine "sensor and actuator";

"Anodic bonding technique under low temperature and low voltage using evaporateti glass", published in Vol. 15, No. 2, March / April 1997, of the "Journal Vacuum Science Technology '';

"Silicon-to-silicon wafer bonding using evaporateti glass", published on page 179 and following, of No. A 70, 1998, of the magazine "Sensor and Actuator".

For completeness, Fig. 5 schematically represents the step of joining the nozzle plate 12 with the substrate 11 by means of the anodic bonding technique, and the anodic welding apparatus or machine, generally indicated with 85, which is used to perform this joint .

In particular, the anodic welding machine 85 comprises two counter-electrodes, indicated with 81 and 82, provided to operate respectively as anode and cathode during the anodic welding phase. In detail, initially the nozzle plate 12 and the substrate 11 are arranged in mutual contact along the smooth surface 79 defined by the borosilicate glass layer 78a, and furthermore precisely aligned with respect to each other. Then, during a spot welding operation, the nozzle plate 12 and the substrate 11 are temporarily connected to each other, for example by means of a laser beam, or by means of a suitable adhesive, so that they are held together, at least until to the realization of the final joint. Then the group formed by the nozzle plate 12 and the substrate 11 is loaded onto the anodic welding machine 85, placing the substrate 11 on a heating element 83 which has the function of heating and maintaining the substrate 11 at a temperature between 200 and 400 ° C, during anodic welding.

furthermore, the unit formed by the nozzle plate 12 and the substrate 11 is arranged on the welding machine 85 by placing the anode 81 of the latter on the nozzle plate 12, with a certain pressure, and further electrically connecting the cathode 82 of the same anodic welding machine 85 with the portion 77a, of the tantalum layer 77, which extends externally to the contact area between the substrate 11 and the nozzle plate 12. In particular, the anode 81 has a plate shape such as to practically cover the nozzle plate 12 for its entire extension.

The cathode 82 of the welding machine 85 is also connected to the main silicon layer of the substrate 11, and to the heater 83, to keep them at the same potential during the welding operation. At this point, the anodic welding machine 85 applies, for example during a period of 15 minutes, a potential defined by a voltage V, indicatively comprised between 50 and 500 volts, between the anode 81 and the cathode 82, thus activating that phenomenon called, as mentioned, anodic welding which determines the structural cohesion between the borosilicate glass of the layer 78a and the silicon oxide SiO2 present along the surface of the nozzle plate 12.

Since the tantalum is conductive, the layer 77 operates during this phase of anodic welding as a real cathode plate which distributes the potential difference generated by the anodic welding machine 85 through the joint area, so that the welding takes on uniform characteristics along the its extension.

Therefore the substrate 11 and the nozzle plate 12 are rigidly and structurally joined by means of a joint, indicated with 25, which extends along a corresponding joint area defined by the layer 78a of borosilicate glass deposited on the substrate 11,.

In this way the ejection head 10 is formed, with the relative internal hydraulic circuit 21 intended to convey the liquid 14 inside the ejection head 10.

The ejection head 10 manufactured in the aforesaid manner with the junction 25 has numerous and important aspects of innovation with respect to the known art.

First of all, unlike what happens in the known art, the substrate 11 and the nozzle plate 12 of the ejection head 10 are intimately joined together with a joining process that does not involve the use of additional substances, such as adhesives or other compounds, generally of an organic type, such as to create a certain structural discontinuity in the junction area.

In fact, the anodic bonding technology, by which the junction 25 is made, is characterized precisely by its ability to achieve complete continuity and structural interpenetration between the materials of the parts that are joined, in this specific case between the silicon constituting the nozzle plate 12 and the borosilicate glass deposited on the substrate 11.

In particular, the structure of the ejection head 10 obtained through the present method does not present, neither in the parts that compose it, nor along the junction 25, substances of an organic type, or other similar materials, so that the ejection head 10 can be advantageously used, without suffering damage, such as corrosion, and / or detachment, which would compromise its operation, even with liquids that are particularly aggressive towards organic compounds.

As a general concept, it can be stated that the ejection head 10 of the invention is characterized in that it comprises, between the nozzle plate 12 and the substrate 11 carrying the ejection actuator 15, a junction 25 which has the property of being substantially inert from a chemical point of view.

In other words, this junction 25, in relation to the liquid 14 which is contained in the hydraulic circuit 21 of the ejection head 10 and which therefore laps the area of the junction 25 to be ejected in the form of drops from the ejection head 10, has special properties of resistance to chemical corrosion by this liquid 14, as well as chemical non-combinability with the latter, which are at least equal and equivalent, and in any case not inferior, to those of the materials, in particular silicon, and / or of the parts that make up the structure of the nozzle plate 12 and of the substrate 11, and which are also lapped by the liquid 14.

Description of a first example of application of the invention to make an inkjet print head

Fig. 6 shows in section an ink jet print head, generically indicated with 110 and suitable to be fed with ink 140, which is made in accordance with the method of the invention. Where possible, the parts of the print head 110 corresponding to those of the ejection head 10 are indicated with numerical references increased by 100 with respect to the ejection head 10.

In particular, the print head 110 comprises a nozzle plate 112 and a substrate 111, also called in English "die", which are manufactured, distinctly from each other, and then rigidly joined together by means of a junction 125, in a similar way. to the manufacturing process described in connection with the ejection head 10. In particular, the junction 125 is made by means of the anodic welding technology, after having suitably prepared the substrate 111 by depositing on it a layer 178 of borosilicate glass.

The substrate 111 and the nozzle plate 112 define a plurality of ejection units, indicated with 110a, 110b, 111c, etc. , which are arranged along an ejection side 150 of the print head 110 and each have a structure corresponding to that of the ejection head 10.

Each ejection unit 110a, 110b, 110c, etc., comprises a respective nozzle, in the order indicated with 113a, 113b, 113c, etc. ; a respective actuator 115a, 115b, 115c, etc. ; and a respective ejection chamber 120a, 120b, 120c, etc.

The print head 110 is also provided internally with a hydraulic circuit 121 which has the function of feeding the ink 140 from a single tank 117 to the various ejection units 110a, 110b, 110c, etc. , and which includes, in addition to chambers 120a, 120b, 120c, etc. , a plurality of supply channels 122, each communicating with a respective ejection chamber 120a, 120b, 120c, etc. , and a centered slot 123 formed through the substrate 111.

In particular, the central slot 123 communicates at one end with the tank 117, and at the opposite end with the plurality of supply channels 122, which in turn are arranged both on one side and on the other of the slot 123 to put the slot 123 communicates with the ejection chambers 120a, 120b, 120c, etc. , of the various ejection units 110a, 110b, 110c, etc.

In this way the ink 140 can flow from the tank 117 to each single ejection unit 110a, 110b, 110c, etc. , through the hydraulic circuit 121. As already mentioned, the method for manufacturing the print head 110 is substantially similar to that for manufacturing the ejector 10.

Again, in order to improve the efficiency of the industrial mass production of these print heads 110, a single silicon wafer can be used both to manufacture a multiplicity of substrates 111, and to manufacture a multiplicity of nozzle plates. 112, with obvious advantages in terms of lower costs in industrial production.

In detail, as schematically represented in Fig. 7, a plurality of nozzle plates 112, corresponding to elementary portions 112a, 112b, 112c, etc. , of an original silicon wafer 151, are made together on this original silicon wafer, through the steps described with reference to the nozzle plate 12, so as to form for each nozzle plate 112 the respective ejection chambers 120a, 120b, 120c, etc. , and the respective nozzles 113a, 113b, 113c, etc. ..

Finally, in accordance with what is indicated by the arrow 160, this wafer 151 is cut or singularized into units, each of which constitutes a nozzle plate 112.

Similarly and as shown in Fig. 8, a plurality of substrates 111, each corresponding to an elementary portion 111a, 111b, 111c, etc. , of a single original wafer of silicon 170, are formed simultaneously on the latter through the steps already described with reference to the substrate 11.

In particular these elementary portions or areas 111 a, 111 b, 111 c, etc. of the silicon wafer 170 are subjected to a series of operations so as to provide, in correspondence with each of them, a structure of the type shown in Fig. 4 - sect. (c), with a layer of borosilicate glass 178 which defines a joint area for the subsequent anodic welding operation.

Conveniently, in order to prepare the silicon wafer 170 for the subsequent joining operation with the anodic welding, the conductive layers of tantalum of the various areas 111 a, 111 b, 111 c, etc. are interconnected with each other and with a conductive ring 177a made along the edge of the wafer 170, so as to form, along the surface of the wafer 170 itself, a mesh 177, which is also called mesh or equipotential network due to its ability to keep the various elementary areas 111 a, 111 b, 111 c, etc. at the same potential. when joining with nozzle plates 112.

An equipotential network of the type of the mesh 177 is described in the Italian patent application No. T099A000987, filed on November 15, 1999 in the name of the Applicant, which application is cited here for reference purposes for every detail, not shown in the present description, on the configuration and characteristics of the mesh 77.

In this way the silicon wafer 170 acquires a structure which integrates a plurality of elementary areas 111a, 111b, 111c, etc. , each corresponding to a substrate 111, which are already prearranged for joining with the respective nozzle plates 112.

Then the individual nozzle plates 112, which, as mentioned, have been manufactured separately, are mounted, aligned, and temporarily fixed, one by one, on the various elementary areas 111a, 111b, 111c, etc. , defined on the silicon wafer 170 and therefore still rigidly connected to each other. At this point it is possible to proceed with the actual anodic welding step, in which each nozzle plate 112 is joined with the corresponding elementary area 111a, 111 b.

111c, etc. of the silicon wafer 170, by applying a certain potential between them by means of a suitable anodic welding machine.

In order to allow a correct support of the anode on the various nozzle plates 112 and therefore their optimal welding with the respective areas 111a, 111b, 111c, etc. of the silicon wafer 170, this anodic welding machine has a suitably modified anode, and in particular divided into a plurality of elements, each corresponding to a nozzle plate 112, which are mounted on a sprung structure such as to allow limited movements between a anode element and another.

In fact, in this way, each of these anode elements is able to adapt, independently of the others, to the corresponding nozzle plate 112, so as to rest perfectly on the latter with the correct pressure, when the anode of the anodic welding machine it is generally brought into contact against the various nozzle plates 112.

In turn, the cathode of the welding machine is put into contact, possibly in several points, with the conductive outer ring 177a, with which the various layers of tantalum, forming the mesh 177 and arranged on the elementary areoles of the silicon wafer 170, are connected.

In this way all these tantalum layers are brought and maintained at the same potential during the anodic welding phase.

In particular, this anodic welding step consists, as already mentioned, in placing each nozzle plate 112 in mutual contact at a given pressure and temperature with the respective area 11a, 111b, 111c, etc. , and in applying a suitable potential between them, by means of the anode which presses with its elements on each nozzle plate 112, and the cathode which is connected, through the mesh 177, with the tantalum layers disposed on each area 111a, 111b, 111c, etc. .

In this way, that intimate structural cohesion, typical of anodic welding technology, is achieved between each nozzle plate 112 and the corresponding elementary area 111a, 111 b, 111 c, etc. of the silicon wafer 170.

Finally, after making the junction, the silicon wafer 170 is cut or singularized into individual blocks, each of which is formed by a nozzle plate 112 and by a substrate 111 rigidly and structurally connected to each other, and constitutes an ejection assembly which is suitable for to be subsequently assembled with a reservoir to form a print head 110 like the one shown in Fig. 6.

The method of the invention makes it possible to produce a print head capable of operating with decidedly more aggressive inks than the neutral ones, generally based on water or alcohol, used on traditional ink jet heads. In fact, the so-called aggressive inks, while they are completely harmless in relation to the head of the invention, have the ability, if used with traditional print heads, to irreparably damage their structure in a very short time, in particular in the area or in the junction areas between the parts that make up the traditional print heads, being, as known, these junctions made with substances that can be easily attacked by and / or can be combined with these aggressive inks. Furthermore, this method, which adopts the anodic welding technology, has the further advantage, compared to traditional methods, of entailing the occurrence of less thermal expansion and in general less deformations during the joining phase between the nozzle plate and the substrate, both of which silicon, to form the inkjet print head.

On the contrary, in the traditional method, the nozzle plate and the substrate, as well as the hydraulic circuit are normally made of different materials, such as for example: metal, silicon, and plastic, so these parts, when connected together to form the head printing, can give rise to reciprocal deformations such as to adversely affect the manufacturing precision of the print head.

Therefore, in summary, the method of the invention makes it possible to respect extremely low manufacturing and assembly tolerances, and therefore to achieve construction accuracies in the production of print heads which are much higher than the traditional method.

Description of a second example of application of the invention concerning an injector for internal combustion engines

Fig. 8 schematically illustrates an application in which the injection head of the invention constitutes a fuel injector for an internal combustion engine, generically indicated with 200, and comprising at least a cylinder 201 with a piston 202 and a combustion chamber 203; a duct 204 for the fresh air supply to the combustion chamber 203, and an exhaust duct 206 for the fumes from the combustion chamber 203.

For simplicity, a single cylinder 201 is shown in Fig. 9. even if it is clear that the engine 200 can comprise a plurality of cylinders, according to typologies widely known in the art.

A valve 207 is arranged at the outlet area of each of the ducts 204 and 206 in the combustion chamber 203, in order to exclude or not the flow of air to and the flow of fumes from the latter. The supply duct 204 is able to receive the air from the filtering area 208, where the fresh air is suitably filtered, and houses inside it a butterfly valve 209 which has the function of controlling the flow of direct filtered air according to the direction of the arrow 205 towards the combustion chamber 203.

The injector, indicated with 210, has the function of ejecting drops of fuel, such as petrol or diesel, into the supply duct 204, in quantities exactly controlled by a control unit 211, associated with the ejector 210, so as to form with the filtered air coming from the filtering zone 206 an air-fuel mixture which feeds the combustion chamber 203.

In particular, the optimal quantities of fuel to be ejected in the form of drops are determined by the control unit 211 on the basis of data sent to the latter, via lines 212, by suitable sensors of the engine.

The injector can be mounted in the position indicated with A, after the butterfly valve 209, in the case of Multipoint injection (also indicated with MPI from the English expression "Multi Point Injection"), that is, with an injector for each cylinder; or also , alternatively, in the position indicated with B, before the throttle 209, in the case of single point injection (SPI), ie with a single injector that generates the air-fuel mixture which is then distributed among the various cylinders. case the ana adduction duct divides into several ducts corresponding to the engine cylinders, immediately after the throttle 209.

In this way, the injector 210 of the invention allows the quantity of fuel delivered to the cylinder (s) of the engine to be metered with great precision, so as to obtain better performance of the same engine, such as for example a higher thermal efficiency, compared to to traditional engines.

Furthermore, the injector has a particularly robust structure and suitable for effectively resisting the system of thermal and mechanical stresses, as well as the corrosive actions of a chemical nature dependent on the fuels used, which are typically present in endothermic engines.

Other possible applications of the injection head according to the invention

The forms of application of the ejection head manufactured in accordance with the present method are not limited to those previously described.

In fact, this ejection head, by virtue of its chemically inert structure in the junction area between the actuation support and the nozzle plate, is suitable for use in a variety of sectors that require precise injection of special liquids, sometimes specifically developed for these sectors, and decidedly more aggressive from a chemical point of view than water-based or even alcohol-based inks, which are usually used for printing on paper supports using conventional inkjet print heads.

In particular, the field of industrial marking in general is mentioned, in which this ejection head could be advantageously used to eject liquids, such as paints or special inks, able to adhere stably even to non-paper supports, such as plastic or metal laminates, to in order to create particular graphics on these supports.

For example, the ejection head could be used to create customized images on plastic supports, such as those that are generically called with the word "badge", or on numerous consumer products, such as skis, helmets, tiles, gift items, and others. still. In fact, the liquids currently used for these marking applications, and probably also those that will be developed in the future, are incompatible with the use on traditional print heads, as they are prepared with substances or solvents that would irreparably damage the structure of these heads. traditional, while on the contrary they could be used without any inconvenience with the present ejection head.

By way of example, some types of solvents are mentioned below which are already widely used in products such as fuels, paints and printing inks, and which could be used to prepare liquids to be used, without problems, in combination with the ejection head. of the invention, thanks to the chemically inert structure of the latter: alitatic and aromatic hydrocarbons such as: liquid paraffins, toluene, xylene;

alitatic and aromatic alcohols such as: methanol, isopropyl alcohol, n-propyl alcohol, secbutyl alcohol, isobutyl alcohol, n-butyl alcohol, benzyl alcohol, cyclohexanol;

esters such as: put acetate, ectacetate, isopropyl acetate, n-propyl acetate, sec-butyl acetate, isobutyl acetate, n-butyl acetate, amyl acetate, 2-ethoxyethyl acetate;

glycoethers such as: 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol;

ketones such as: acetone, methyl ethyl ketane, put isobutyl ketane, methyl isoamyl ketane,

cyclohexanone;

lactones such as: 6-caprolactone monomer.

Another possible application of the present ejection head is that of microdosing, in particular but not exclusively in the biomedical sector. In fact, this ejection head, thanks to its chemically inert structure and free of organic substances, can be used without problems to eject and dose a wide range of liquids used in the medical field, for example in general organic liquids and more particularly liquids containing urea. , or liquids such as insulin, or still other medical liquids that need to be dosed with particular precision in certain medical functions. The use of the present ejection head for ejecting edible liquids, that is food-grade liquids, in a controlled manner, can also be included among the possible forms of application of the invention. In general it can be said that this ejection head has a structure, chemically inert, which, in addition to the advantage of not being corrodible by a wide range of liquids used in the medical field, also has the further advantage of not combining with such liquids, and therefore not to alter and offend even minimally their characteristics while they are stored in this ejection head.

It is understood that modifications and / or improvements may be made to the method for manufacturing a liquid ejection head in the form of drops, as well as to the ejection head manufactured in accordance with this method, described up to now, without departing from the scope of the present invention.

Claims (31)

CLAIMS 1. Method for manufacturing an ejection head (10; 110), or ejector, suitable for ejecting a liquid (14; 140} in the form of drops (16), and having a hydraulic circuit inside it (21; 121 ) for containing and conveying said liquid (14; 140), comprising the following steps: manufacturing a nozzle plate (12; 112) having at least one ejection nozzle (13; 113a, 113b, 113c); manufacturing a substrate (11; 111) or actuation support having at least one actuator (15; 115a, 115b, 115c) for activating the ejection of said drops (16) of liquid through said at least one nozzle (13; 113a, 113b, 113c); And integrally joining said nozzle plate (12; 112) and said substrate (11; 111) to each other to form said ejection head (10; 110) together with the relative hydraulic circuit (21; 121), in which said joining step comprises the realization of a junction (25; 125), between said nozzle plate (12) and said substrate (11), designed to be lapped by said liquid (14; 140) contained in the hydraulic circuit (25; 125), characterized in that said junction (25; 125) is chemically inert in relation to said liquid (14; 140) to an extent at least equal to, and in any case not less than, the materials and / or parts of said nozzle plate (12; 112) ) and of said substrate (11; 111), which are intended to be lapped by said liquid (14; 140). 2. Method for manufacturing an ejection head according to claim 1, characterized in that both said nozzle plate (12; 112) and said substrate (11; 111) consist essentially of silicon, each of them being made of starting from a respective silicon wafer (51, 70; 151, 170). 3. Method for manufacturing an ejection head according to claim 1, characterized in that said joint (25; 125) is made by means of the so-called anodic bonding technology. 4. Method for manufacturing an ejection head according to claim 3, characterized in that it comprises, for the purpose of preparing said substrate (11; 111) and said nozzle plate (12; 112) to be joined by said welding technology anodic, a preliminary step of depositing a layer of borosilicate glass (78; 178) on the outer surface of either said substrate or said nozzle plate. 5. Method for the manufacture of an ejection head according to claim 4, characterized in that said layer of borosilicate glass (78) is constituted by Pyrex containing sodium. 6. Method for manufacturing an ejection head according to claim 4, characterized in that it comprises a planarization step (CMP) for planarizing said layer of borosilicate glass (78) along the free surface intended to couple with said nozzle plate ( 12). 7. Method for manufacturing an ejection head according to claim 4, characterized in that it comprises, following said preliminary step, a step of etching said layer of borosilicate glass (78; 178) to uncover the area of said actuator ( 15; 115a, 115b, 115c) and define the junction areas (78a) between said substrate (11; 111) and said nozzle plate (12; 112). Method for manufacturing an ejection head according to claim 7, wherein said substrate (11; 111) is provided with a protective conductive layer (77; 177), which extends over the region of said actuator (15 ; 115a, 115b, 115c), and on which said layer of borosilicate glass (78; 178) is deposited, characterized by this the anodic welding between said nozzle plate (12; 112) and said substrate (11; 111) is achieved by connecting said nozzle plate (12) and said conductive layer (77) respectively to a first (81) and to a second counter electrode (82) of a suitable anodic welding machine (85), and then applying a specific voltage between said counterelectrodes (81, 82). 9. Method for manufacturing an ejection head according to claim 8, characterized in that said first counter electrode (81) is formed by a plate resting on said nozzle plate (12) along the side bearing said ejection nozzle (13) and from what, during the anodic welding step, said first counter electrode (81) operates as an anode, while said second counter electrode (82) operates as a cathode. 10. Method for manufacturing an ejection head according to claim 8, characterized in that, during said anodic welding, said substrate (11) is kept at a predetermined temperature by means of a heating element (83). 11. Method for manufacturing an ejection head according to claim 8 or 9, wherein said actuator (15; 115a, 115b, 115c) is of the thermal type and in particular consists of a resistor (74) which is adapted to heating rapidly to generate, inside said liquid, a vapor bubble such as to cause the ejection of said drops, characterized by what said conductive protective layer (77; 177) is made with tantalum (Ta). Method for manufacturing an ejection head according to claim 8, characterized in that said conductive layer (77) is made with a portion (77a) extending, along said substrate (11), outside the area of junction between the latter and said nozzle plate (12), and which has the purpose of allowing the connection between said conductive layer (77) and said second counter-electrode (82) of said special anodic welding machine (85). 13. Ejection head (10; 110), or ejector, adapted to eject a liquid (14; 140) in the form of drops (16), comprising; a nozzle plate (12; 112) having at least one ejection nozzle (13; 113a, 113b, 113c); a substrate (11; 111) or actuation support having at least one actuator (15; 115a, 115b, 115c) for activating the ejection of said drops (16) of liquid through said at least one nozzle (13; 113a, 113b, 113c) ); a hydraulic circuit (21; 121) to contain and convey said liquid inside said ejection head (10; 110); And a junction (25; 125) which joins said nozzle plate (12; 112) and said substrate (11; 111) integrally with each other and which is designed to be lapped by the liquid (14) contained in said hydraulic circuit (25; 125) , characterized in that said junction (25; 125) is chemically inert in relation to said liquid to an extent at least equal to, and in any case not less than, the materials and / or parts that make up the structure of said nozzle plate (12; 112) and of said substrate (11; 111) and which are intended to be lapped by said liquid (14; 140). 14. Ejection head according to claim 13, characterized in that both said nozzle plate (12) and said substrate (11) are essentially constituted of silicon, each of them being made starting from a respective silicon wafer (51, 70). 15. Ejection head according to claim 13 or 14, characterized in that said joint (25; 125) is made by means of the so-called anodic bonding technology. 16. Ejection head according to claim 15, characterized in that it comprises, in the junction area between said substrate (11) and said nozzle plate (12), a layer of borosilicate glass (78, 78a) which has been previously deposited on the external surface either of said substrate (11) or of said nozzle plate (12) to prepare them for the junction by means of said anodic welding. 17. Ejection head according to claim 15, wherein said substrate (11) is provided with a protective conductive layer (77) to protect said actuator (15), characterized by this said conductive layer (77) extends, as well as along the actuator zone (15), also along the junction (25) between said substrate (11) and said nozzle plate (12), and further comprises a portion (77a) disposed externally with respect to the area of said junction (25), in which this portion (77a) has the function of allowing, during the manufacture of said ejection head (10), the electrical connection between said conductive layer (77) and a counter-electrode (82) of a suitable machine (85) used to realize said joint (25) by means of said anodic welding technology, applying a suitable potential (V) between said substrate and said nozzle plate. 18. Ejection head according to claim 13, characterized in that it has a structure that is chemically inert in relation to a liquid prepared with a solvent which can be selected from a group consisting of: alitatic and aromatic hydrocarbons such as: liquid paraffins, or toluene, or xylene; aliphatic and aromatic alcohols such as: methanol, or isopropyl alcohol, or n-propyl alcohol, or sec-butyl alcohol, or isobutyl alcohol, or n-butyl alcohol, or benzyl alcohol, or cicohexanol; esters such as: methyl acetate, or ethyl acetate, or isopropyl acetate, or n-propyl acetate, or sec-butyl acetate, or isobutyl acetate, or n-butyl acetate, or amyl acetate, or 2-ethoxyethyl acetate; glycoethers such as: 2-methoxyethanol, or 2-ethoxyethanol, or 2-butoxyethanol; ketones such as: acetone, or methyl ethyl ketone, or methyl isobutyl ketone, or methyl isoamyl ketane, or dclohexanone; And lactones such as β-caprolactone monomer. 19. Print head for ejection of ink drops characterized in that it consists of an ejection head (110) according to claim 13, whereby said print head (110), by virtue of said junction (125) chemically inert, it is particularly suitable for use with inks (140) having a high chemical aggressiveness. 20. Injector (210) for drops of fuel, such as for example petrol or diesel, in an internal combustion engine, characterized in that it consists of an ejection head according to claim 13. A fuel droplet injector (210) according to claim 20, wherein said engine comprises at least one cylinder, an air supply duct for said cylinder, and a valve for regulating the flow of air through said supply duct. , characterized in that said fuel injector is arranged along said supply duct downstream of said regulating valve, if a specific injector is associated with each cylinder of said engine to generate the air-fuel mixture fed to each single cylinder; or it is arranged upstream of said regulating valve, if a single injector is provided to centrally generate the air-fuel mixture to be subsequently distributed to the various cylinders of said engine. 22. Method for manufacturing an ink jet print head (110) having internally a hydraulic circuit (121) for containing and conveying said ink (140), comprising the following steps: manufacturing a nozzle plate (112) having at least one ejection nozzle (113a, 113b, 113c); manufacturing a substrate (111) having at least one actuator (115a, 115b, 115c) for activating the ejection of said ink (140), in the form of drops, through said at least one nozzle (113a, 113b, 113c); And integrally joining said nozzle plate (112) and said substrate (111) together to form said print head (110), together with said hydraulic circuit (121), in which said joining step comprises making a joint (125) , between said nozzle plate (112) and said substrate (111), designed to be lapped by the Ink (140) contained in the hydraulic circuit (121), characterized in that said junction (125) is chemically inert in relation to said liquid To an extent at least equal to, and in any case not less than, the materials and / or parts, making up the structure of said nozzle plate (112) and of said substrate ( 11; 111), which are expected to be (coveted by said ink (140). 23. Method for manufacturing an ink jet print head (110) according to claim 22, characterized by what said junction (125) is made by means of the so-called anodic bonding technology or "anodic bonding". Method for manufacturing an inkjet print head (110) according to claim 23, characterized in that it comprises, in order to prepare said substrate (111) and said nozzle plate (112) to be joined by said anodic welding technology, a preliminary step of depositing a layer of borosilicate glass (178) on the external surface either of said substrate or of said nozzle plate, in correspondence with the junction area (125). Method for manufacturing an inkjet print head (110) according to claim 23, characterized in that it comprises a step (CMP) for planarizing the surfaces of said substrate and / or said nozzle plate in a manner to be prepared for the joining phase by means of said anodic welding technology. 26. Method for manufacturing an inkjet print head (110) according to claim 23, characterized in that said step of manufacturing a nozzle plate (112) includes the following steps: providing a silicon wafer (151) comprising a plurality of elementary areas (112a, 112b, 112b) each corresponding to a nozzle plate; forming by incision, on each of said areas, at least one chamber (120a; 120b; 120c) and a supply duct (122) of the hydraulic circuit (121) of the corresponding nozzle plate (112), said supply duct (122) being provided for supplying the ink (140) to said chamber (120a; 120b; 120c); And dividing said silicon wafer into elementary units each constituting a nozzle plate (112). Method for manufacturing an inkjet print head (110) according to claim 26, characterized in that said silicon wafer is of the thin type and has an indicative thickness of 75 μm. 28. Method for the manufacture of an ink jet print head (110) according to claim 23, characterized in that it comprises the following steps: providing a silicon wafer (170) comprising a plurality of elementary areas (111a, 11 b, 111 c) each corresponding to a substrate (111); arrange, on said silicon wafer (170), a protective layer of conductive material consisting of a plurality of mutually interconnected portions so as to form an equipotential mesh or network (177), in which each portion of said conductive layer is deposited on top a respective elementary area (111a, 11b, 111c) of said silicon wafer (170), and extends both along the area of said actuator (115a, 115b, 115c) for the purpose of protecting it, and along the junction area (125) which will be subsequently formed between the substrate (111) and the nozzle plate (112), and furthermore also externally to said junction area (125); arrange a plurality of nozzle plates (112), manufactured separately with respect to said substrate (111), along said silicon wafer (170), with each nozzle plate (112) in contact with a corresponding elementary area of said silicon wafer (170 ); connecting said equipotential network with a counter-electrode of a suitable anodic welding machine; apply, by means of said counter-electrode, a suitable potential between said equipotential network and each nozzle plate (112) to realize said junction (125), based on the anodic welding technology, between each elementary area (111a, 11b, 111c) of said silicon wafer (170), and the corresponding nozzle plate (112), e divide said silicon wafer (170) into a plurality of units, each formed by a single substrate and a single nozzle plate, and constituting an ink jet print head. Method for manufacturing an inkjet print head (110) according to claim 28, characterized in that said protective layer is made with tantalum (Ta). Method for manufacturing an inkjet print head (110) according to claim 28, characterized in that it comprises, after said step, arranging a plurality of nozzle plates (112) on said silicon wafer (170 ), a step of temporarily bonding with an adhesive each of said nozzle plates (112) with the corresponding elemental area (111a, 11b, 111c) of said silicon wafer (170). 31. Method for manufacturing an ejection head and an inkjet print head, and corresponding ejection head (10) and print head (110) substantially as described with reference to the attached drawings.